% square lattice (width #1, height #2, origin #3)
\def\grid#1#2#3{
  \foreach\i in {0,...,#2}{
    \draw#3++(0,\i)--++(#1,0);
  }
  \foreach\i in {0,...,#1}{
    \draw#3++(\i,0)--++(0,#2);
  }
}

% dimer (bottom-left vertex #1, vertical or horizontal #2)
\def\dimer#1#2{
  \if#2h
    \draw[line width=5pt]#1--++(1,0);
    \fill#1circle(7pt);
    \fill#1++(1,0)circle(7pt);
  \else
    \draw[line width=5pt]#1--++(0,1);
    \fill#1circle(7pt);
    \fill#1++(0,1)circle(7pt);
  \fi
}

% interactions (bottom-left vertex #1, vertical or horizontal #2)
\def\interaction#1#2{
  \if#2h
    \draw[line width=5pt, color=white]#1--++(1,0);
    \draw[line width=4pt, decorate, decoration={snake}, color=red]#1--++(1,0);
  \else
    \draw[line width=5pt, color=white]#1--++(0,1);
    \draw[line width=4pt, decorate, decoration={snake}, color=red]#1--++(0,1);
  \fi
}